Today many network operators have a deployed ring-based network but state that they see “mesh” as the way to go in future with DWDM-based optical networking . It is generally recognized that while rings have been a practical and economic alternative, especially in metro networks, ring networks consume a lot of transmission capacity, making them less suitable for long-haul applications. We have previously analyzed that even efficiently designed ring networks may embody total capacity that is up to three times the shortest-path capacity for the amount of demand they serve.
Ring protection capacity is a source of 100% minimum redundancy, but the efficient utilization of working capacity tends to also be limited by ring loading and “stranded capacity” issues. Additionally demand routing can rarely follow the true shortest path over the facilities graph. At the same time as rings are locking up so much physical transport capacity, some operators can barely deploy new capacity fast enough to keep up with demand. In circumstances of such rapid growth, transport efficiency is important: Even if the cost of the capacity was zero, more efficient transport architectures can serve more revenue-bearing demand for the same installed base of transmission systems.
One method of increasing reliability of a ring such as a SONET ring is proposed in U.S. Pat. No. 6,370,110 issued Apr. 9, 2002. In this patent, a ring is connected, or interworked, with a mesh to access each other's protection capacity. Both ring and mesh continue to exist, and to operate individually as ring and mesh. The only change is that if needed the ring protection channels are made available to the mesh, and vice versa. The method proposed in this patent, however, does not deal with a ring to mesh conversion directed to serving an increased amount of demand.